The invention relates to a device for a drilling rig for forming of a borehole in a subterranean structure, where the drilling rig comprises a first top driven drilling machine arranged vertically displaceable along a guide track, more particularly in that a second drilling machine is arranged between the first drilling machine and the bore hole vertically displaceable along a guide track and provided with a rotary table arranged to be able to take the weight of a pipe string, a rotary drive unit arranged for continuous rotation of the pipe string, a fluid chamber arranged to in a fluid communicating manner to connect a pipe string end portion with a drilling fluid plant, as the fluid chamber is provided with pipe string ports comprising means arranged to in a fluid sealing manner to close the pipe string ports, and a power tong arranged for continuous rotation of an element connected to the pipe string, as the power tong is arranged in the fluid chamber. Also described is a method for drilling with continuous tool rotation and continuous drilling fluid supply.
During drilling in the underground, such as in exploration and production drilling in connection with exploitation of oil and gas, new sections of drill pipe are steadily joined as the hole is extended. In every such operation the rotation of the pipe string is stopped, and in most techniques in use, the circulation of drilling liquid is simultaneously stopped while the pipe string is extended. The drawback of such disruption in the rotation and drilling liquid circulation is well known within the industry. The transport of cuttings out of the well is stopped, and the cuttings will thereby start to sink, and in horizontal bore hole portions the cuttings may sediment. This may bring about time loss in that drilling liquid must be circulated for some time before the drilling operation is restarted to clean up the bore hole. When the pipe string rotation is stopped, the risk of the pipe string getting stuck in the bore hole is also increased due to collection of the sinking cuttings and increased friction against the formation wall as a consequence of the pressure difference between the bore hole and the formation around the hole. A further drawback is that a stop in the drilling liquid circulation leads to pressure variations in the drilling liquid, and if the pressure comes outside critical limits, the formation fluid may get into the bore hole or drilling liquid may get out into the formation, and both situations are undesirable.
From NO326427 is known a device for a top drive where a drive shaft arranged for releasable connection to a drive gear and with a first end portion of a drill pipe, is provided with a central run therethrough arranged for fluid communication between the drilling liquid plant and a fluid run in the drill pipe. A first and a second releasable, drive shaft enclosing or pipe string enclosing, respectively, pressure seal and a valve arranged for in an open position to provide a passage for the drill pipe or the drive shaft, form a first and a second chamber. A drilling liquid inlet is allocated to the second chamber and is arranged for fluid communication between the drilling liquid plant and the coupling housing. Thereby is provided a possibility for continuous drilling liquid circulation, but at installation of a new drill pipe section the pipe string rotation has to be stopped.
GB 2399112 describes a method and an apparatus for connecting pipe components during drilling without the pipe string rotation or the fluid circulation through the pipe string is stopped. This is achieved by cooperation between a top drive and a rotary table. A fluid circulation device being joined to the threaded portion on the pipe components is used for fluid circulation when the top drive is disconnected from the pipe string.
U.S. Pat. No. 6,412,554 describes a system for continuous circulation of fluid to and through a pipe string, for example a coiled tubing or a pipe string made up of pipe sections screwed together. The system comprises an upper and a lower chamber having through openings for receiving the pipe string, as sealing devices are arranged at an upper and a lower opening and is arranged to fit tightly around the pipe string. The system also comprises devices for rotation and axial displacement of the pipe string or pipe components relative to the chambers.